(1) Field of the Invention
The present invention relates to a method of bonding molded articles comprised of a 4-methyl-1-pentene polymer to each other or bonding a molded article comprised of a 4-methyl-1-pentene polymer to a molded article comprised of a vinyl alcohol type polymer, metal or glass. More particularly, the present invention relates to an improvement of this bonding method in which the adhesion strength can be enhanced.
(2) Description of the Prior Art
4-Methyl-1-pentene polymers are excellent in the heat resistance, transparency and other properties. Accordingly, these polymers are widely used for the manufacture of vessels for physical and chemical experiments, table wares for electronic oven treatments, percolators, syringes for medical treatments and paper coatings for food vessels. Although 4-methyl-1-pentene polymers are excellent in the heat resistance and other properties, they are somewhat defective in the moldability because the melting point is high. Therefore, it is very difficult to prepare a molded article having a complicated configuration directly from a 4-methyl-1-pentene polymer according to the melt-molding method.
Accordingly, in order to obtain an article having a complicated configuration from a 4-methyl-1-pentene polymer, it is inevitably necessary to bond molded articles comprised of a 4-methyl-1-pentene polymer to each other. So far as we know, there has not been developed a technique capable of providing a bonding having an adhesion strength of a practical level of at least about 5 Kg/cm.sup.2 in bonding molded articles comprised of a 4-methyl-1-pentene polymer to each other.
Furthermore, 4-methyl-1-pentene polymers are defective in that the adhesion to other materials such as metals is inferior. Accordingly, expansion of the application fields of 4-methyl-1-pentene polymers is restricted by such poor adhesion.
The gas barrier property of a 4-methyl-1-pentene polymer is inferior to that of other polyolefin such as polyethylene, polypropylene or poly-1-butene. Accordingly, the 4-methyl-1-pentene polymer is hardly used as an ordinary packing material. As means for improving the gas barrier property or surface hardness in the 4-methyl-1-pentene polymer while retaining excellent characteristics of this polymer, there is adopted a method in which other material such as polyvinyl chloride, nylon, vinyl alcohol type polymer, metal, glass or the like is laminated on the 4-methyl-1-pentene polymer. In this method, it is necessary to form a bonding having a strength sufficient to resist practical applications between the 4-methyl-1-pentene polymer and the laminated material.
For bonding a polyolefin to other material, there has been adopted a method in which the polyolefin is modified with a carboxylic acid or the like to impart polar groups to the polyolefin and improve the adhesion of the polyolefin to other material. However, even if such modified polyolefin is used, a practical adhesion strength cannot be obtained at normal temperatures, and in order to obtain a practical adhesion strength, it is necessary to perform the bonding operation at a temperature higher than the softening point of the modified polyolefin. This problem is especially serious in case of a 4-methyl-1-pentene polymer, because the softening point and melting point of this polymer are much higher than those of other polyolefins and the bonding operation should be carried out at much higher temperatures for obtaining a practical adhesion strength.